The present invention relates to power tongs utilized to make up or break apart pipe members and, more particularly, relates to back-up tongs utilized to secure a pipe member against rotation. The present invention also relates to tongs of the scissors type, wherein an upper body portion rotates relative to a lower body portion to achieve the high make up or break out torques commonly required for drill pipe.
Rotary power tongs are commonly used to rotate an upper tubular member, e.g., casing, drill pipe, or tubing, relative to a stationary lower tubular member, and thus threadably make up or break apart such members. When employing such powered rotary tongs, it is generally desirable to actively preclude the lower tubular member from rotation, which might otherwise occur as high torque is applied to the upper tubular member by the powered rotary tong during the initial break out or the final make up operation.
Both manual and powered back-up tongs have been utilized to grip and prevent rotation of the lower pipe. Power back-up tongs are generally preferred by tong operators over manual back-up tongs; examples of the latter tongs are described in U.S. Pat. Nos. 2,668,689 and 3,380,323. Such manual tongs generally require additional operator tasks, and may be unable to successfully grip the lower pipe against rotation when the upper pipe is subjected to high torques.
Powered back-up tongs are shown in U.S. Pat. Nos. 2,544,639 and 4,402,239, as well as U.K. Pat. No. 1,348,954. A disadvantage of such back-up tongs, however, is that the external force utilized to adequately grip the pipe to prevent rotation may apply so great a biting force as to crush the pipe. Also, closed throat back-up tongs as shown in U.S. Pat. No. 3,518,903 tend to require a great deal of field adjustment, thereby delaying the costly petroleum recovery operation, and cannot be laterally put on and taken off a section of pipe. An improved back-up tong is described in U.S. Pat. No. 4,290,304. This patent discloses a cage plate assembly which may be rotated by a hydraulic motor carrying a plurality of heads. As the cage plate assembly rotates, the heads are driven inwardly to engage the pipe by cam surfaces on a cam ring affixed to the tong body. The tong utilizes a backing lug affixed to the tong body and a backing pin assembly mounted to the cage plate to automatically align the cage plate opening with the opening in the tong body, so that the tong can be laterally put on and taken off a pipe.
Prior art tongs also include tongs generally referred to as scissors tongs, wherein the upper tong body grips an upper section of pipe, a lower tong body grips a lower section of pipe, and the bodies are then rotated relative to each other to obtain threading or unthreading of the pipe. Generally, only 10.degree.-20.degree. of rotation is provided for in a single scissors or rachet action, so that scissors tongs are generally utilized only for the final make up and break out torques required for certain drill pipe operations. Spinners are thus frequently utilized to thread the drill pipe sections to each other, and the scissors tong is employed for only the final 30.degree. make up rotation or the initial 30.degree. break out rotation requiring extremely high torques. Spinners and scissors type tongs may be combined in a single product, as shown in U.S. Pat. Nos. 2,705,614, 3,629,927, and 3,799,009.
Early embodiments of scissors-type tongs are shown in U.S. Pat. Nos. 2,737,839 and 2,871,743, wherein pivotable levers act to engage each section of pipe. A variation of a scissors-type tong is shown in U.S. Pat. No. 2,760,392, whereby the upper and lower yoke members rotate relative to each other.
A disadvantage of many of the above-referenced scissors-type tongs is that numerous operator actions are required to perform the make-up or break out operation. Scissors-type tongs may also suffer from the drawbacks previously noted in connection with certain back-up tongs, in that the power means utilized to successfully grip the pipe to prevent rotation between the heads and the pipe may be so severe that the heads crush or damage the pipe. Finally, scissors-type tongs typically employ additional mechanisms for aligning the open throat portions of the tongs, but such additional mechanisms may require further operator action or may lack reliability, so that the tongs cannot be easily and reliably put on or taken off a pipe by movement in the lateral direction.
More conventional scissors-type tongs are shown and described in U.S. Pat. Nos. 3,921,473 and 4,082,017. It should be understood that in a conventional scissors-type tong as shown in the latter patent, the upper and the lower tong portions each act to grip the upper and lower pipe sections, respectively. As shown in U.S. Pat. No. 4,082,017, the upper and lower tong sections are rotated by a cylinder interconnected between the tong sections.